There is a need for high power laser beams with specific frequency and phase front requirements for use in the defense industry and for other applications. One means of modifying the frequency and phase front of a laser beam is by use of a Raman amplifier.
Raman amplifiers exist having either collinear or crossed pump and Stokes beams. The crossed-beam geometry, however, only works well for narrow pump band spectra, which severely limits the possibilities for pump lasers.
Wide angle crossed-beam Raman amplifiers have important advantages over collinear beam Raman amplifiers: better transverse intensity homogeneity in the Stokes output, reduced phase aberration, ease of combining the seed with one or more pump inputs and avoidance of competing nonlinear processes having near-collinear phase matching angles. In the past, despite their intrinsic advantages, the use of crossed-beam Raman amplifiers has been restricted to much narrower pump band spectra than for collinear Raman amplifiers, which has limited their applicability.